Film bulk acoustic wave resonators (FBARs) are widely known as thin film piezoelectric bulk acoustic wave resonators. Radial extension mode resonators (RE resonators) that vibrate in radial extension mode (hereafter referred to as “RE mode”) with their center used as a vibration node and ring resonators are also known. Any of these resonators includes a piezoelectric material and metal electrodes provided on and below the piezoelectric material.
Disclosed in U.S. Pat. No. 6,617,249 issued to Ruby et al. on Sep. 9, 2003 is an FBAR that is able to shift a resonant frequency from others by additionally providing an auxiliary metal layer on a surface electrode layer, in order to manufacture resonators having different resonant frequencies.
Disclosed in “Single-Chip Multiple-Frequency RF Micro resonators Based on Aluminum Nitride Contour-Mode and FBAR Technologies” (G. Piazza et al., Proc. IEEE Ultrason. Symp., 18-21 Sep. 2005, pp. 1187-1190) is a ring resonator that is able to shift a resonant frequency from others by adjusting a mask size.
Disclosed in Japanese Patent Application Laid-Open Publication No. 10-256618 are a method for supporting multiple vibrators that vibrate in RE mode, at their centers and a method for supporting an RE resonator in which wiring is connected to an electrode at such a center.
Disclosed in Japanese Patent Application Laid-Open No. 2005-277861 is a microresonator that includes multiple resonators and corresponding multiple electrodes provided outside plane directions of these resonators and in which the resonators supported at their center serving as a vibration node vibrate in a direction perpendicular to the plane directions by Coulomb's force.
Disclosed in “Bulk-Acoustic Wave Filters: Performance Optimization and Volume Manufacturing” (Aigner et al., 2003 IEEE MTT-S digest, pp. 2001-2004) is a thin film piezoelectric bulk acoustic wave resonator that uses a Bragg elastic reflection layer as an elastic insulating layer of an FBAR.